Quantum-limited noise performance of a mode-locked laser diode

Low-noise operation of a 9-GHz hybridly mode-locked laser diode is demonstrated. The integrated timing jitter was 47 fs (10 Hz to 10 MHz) and 86 fs (10 Hz to 4.5 GHz), with a pulse width of 6.7 ps. The noise performance as a function of filter bandwidth and oscillator noise is also addressed.     

Unusual conformational preferences of 1,3‐dimethyl‐3‐isopropoxy‐3‐silapiperidine

The conformational analysis of the first representative of the Si‐alkoxy substituted six‐membered Si,N‐heterocycles, 1,3‐dimethyl‐3‐isopropoxy‐3‐silapiperidine, was performed by low‐temperature ¹H and ¹³C NMR spectroscopy and DFT theoretical calculations. In contrast to the expectations from the conformational energies of methyl and alkoxy substituents, the Me_axi‐PrO_eq conformer was found to predominate in the conformational equilibrium in the ratio Me_axi‐PrO_eq : Me_eqi‐PrO_ax of ca. 2 : 1 as from the ¹H and ¹³C NMR study. The thermodynamic parameters obtained by the complete line shape analysis showed that the main contribution to the barrier to ring inversion originates from the entropy term of the free energy of activation. Copyright © 2012 John Wiley & Sons, Ltd.     

Cyclobutadiene dianion derivatives – Planar 4c,6e or three-dimensional 6c,6e aromaticity?

The spatial magnetic properties (Through Space NMR Shieldings – TSNMRS) of two cyclobutadiene derivatives (2 and 5) and of a number of cyclobutadiene dianion derivatives (3, 4 and 6–8) have been calculated by the GIAO perturbation method employing the Nucleus-Independent Chemical Shift (NICS) concept of P. v. Ragué Schleyer, and visualized as Iso-Chemical-Shielding Surfaces (ICSS) of various size and direction. TSNMRS values can be successfully employed to quantify and visualize the (anti)aromaticity of the compounds studied and to discuss the influence of Li⁺ complexation to cyclobutadiene dianion (4a, 7 and 8) on planar 4c,6e or three-dimensional 6c,6e aromaticity.     

Ab initio study of the substituent effects on the relative stability of the E and Z conformers of phenyl esters. Stereoelectronic effects on the reactivity of the carbonyl group

Equilibria between the Z (tau1= 0 degrees) and E (tau1= 180 degrees) conformers of p-substituted phenyl acetates 4 and trifluoroacetates 5 (X = OMe, Me, H, Cl, CN, NO2) were studied by ab initio calculations at the HF/6-31G* and MP2/6-31G* levels of theory. The preference for the Z conformer, DeltaE(HF), was calculated to be 5.36 kcal mol(-1) and 7.50 kcal mol(-1) for phenyl acetate and phenyl trifluoroacetate (i.e., with X = H), respectively. The increasing electron-withdrawing ability of the phenyl substituent X increases the preference of the Z conformer. An excellent correlation with a negative slope was observed for both series between DeltaE of the E-Z equilibrium and the Hammett sigma constant. By using an appropriate isodesmic reaction, it was shown that electron-withdrawing substituents decrease the stability of both conformers, but the effect is higher with the E conformer. Electron-withdrawing phenyl substituents decrease the delocalization of the lone pair of the ether oxygen to the C=O antibonding orbital (nO--> pi*C=O) in both the E and Z forms and in both series studied; this effect is higher in the E conformer than in the Z conformer. The nO --> pi*C=O electron donation has a minimum value with tau1= 90 degrees and a maximum value with tau1= 0 degrees (the Z conformer), the value with tau1= 180 degrees (the E conformer) being between these two values, obviously due to steric hindrance. The effects of the phenyl substituents on the reactivity of the esters studied are discussed in terms of molecular orbital interactions. ED/EW substituents adjust the availability of the pi*C=O antibonding orbital to interact with the lone pair orbital of the attacking nucleophile and therefore affect the reactivity: EW substituents increase and ED substituents decrease it. Excellent correlations were observed between the rate coefficients of nucleophilic acyl substitutions and pi*C=O occupancies of the ester series 4 and 5.     

Quantitative Bestimmung von Cyanidionen in Gegenwart von Hexacyanoferrationen

Zusammenfassung Es wird auf eine Methode hingewiesen, die es ermöglicht, in Gaswerks- und Kokereiabwässern hohe, geringe und geringste Cyanid-Ionenkonzentrationen in Gegenwart von Hexacyanoferraten quantitativ exakt zu erfassen. Die Ergebnisse werden mit denen der in dieser Zeitschrift³ dargelegten Methoden verglichen.

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Summary A method is recommended for the exact quantitative determination of high, law, and lowest concentrations of cyanide in presence of hexacyanoferrates in effluents from gas works and coke-oven plants. The results are compared with those of a method published earlier in this journal³.

     

Improved STR typing of telogen hair root and hair shaft DNA

Today the STR typing of telogen hair and hair shafts is regarded as a challenge. The small DNA quantity in the hair is highly degraded. Another problem are PCR inhibitors in the hair. In particular hair pigments, the melanins, are known to inhibit PCR. Hairs are exposed to sunlight and partly to chemical oxidation processes, which make them even more difficult to analyze. To increase the chances of a correct typing of hair, the small amount of DNA must be successfully isolated and the inhibitors have to be removed or neutralized. Furthermore, miniSTR typing improves the analysis of stains with degraded DNA like it is the case with hair. We introduce a nonorganic extraction method and in addition a miniSTR concept which is promising in typing stains with little and degraded DNA, especially hairs. The miniSTR concept including five database STRs (SE33, VWA, TH01, FGA, D3S1358) and the gender typing system Amelogenin was optimized for the amplification of hair DNA. Compared to commercial STR kits, this approach resulted in considerably higher success rates.     

Stability of Liquid Layers on Solid Materials

For a class of disjoining pressure potentials the existence of stable liquid layers on solid surfaces is studied. In some cases of solid configurations with simple geometries explicit results are obtained, in particular for a single cylindrical or spherical cavity. No smallness for the thickness of the layer is assumed.     

基于锗硅芯片的光电子学前景与挑战

作为微电子材料,硅具备许多优良的电学特性．采用硅材料的器件集成度能够比其他材料高几个数量级。然而．硅是一种间接带隙材料,其光学跃迁过程会引入大量低能的声子造成跃迁几率很低．导致其光学特性（发射与吸收）远不如Ⅲ/Ⅴ族半导体材料。     

Strukturelle Abwandlungen anN-Acetylneuraminsäure, 3

From methyl-5-acetylamino-7,8-anhydro-4,9-O-bis-(t-butyldimethylsilyl)-3,5-dideoxy--D-glycero-D-galacto-2-nonulopyranosidonic acid methylester (1) the derivatives1 a and1 b were obtained by removing the 9-O-(t-butyldimethylsilyl)group withBu ₄NF, followed by acetylation. Treatment of1 b with 80% acetic acid and acetanhydride/pyridine yields the 8-epi-N-acetylneuraminic acid derivative2 a and the 7-epi-N-acetylneuraminic acid derivative3 a in a ratio of 3:1 (Scheme 1). The structure elucidation of2 b was achieved by converting2 b via the 4,9-bis-O-(tBDMSi)-8-O-tosyl-derivative2 d into the epoxide1 (Scheme 2). Using the same sequence the epoxides4 and5 were transformed into theN-acetylneuraminic acid derivative6 a and the 7,8-bis-epi-N-acetylneuraminic acid derivative7 a (Scheme 3). After treatment with sodium hydroxide and 0.025m HCl and Dowex 50 H⁺ the 8-epi-, 7-epi- and 7,8-bis-epi-N-acetylneuraminic acids2,3, and7 were obtained. These three compounds were tested withCMP-N-acetylneuraminic acid synthetase.

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